Ink compositions involving near-infrared absorber dyes and use in ink jet printing devices

An ink composition including a near infrared absorbing dye that converts absorbed near infrared radiation into heat without fluorescing significantly and a substantially non-aqueous, organic solvent system. The dye is a tetrakis (dialkylaminophenyl) aminium dye coupled with one anion, a cyanine or a squarylium. The non-aqueous, organic solvent system includes an alcohol, for example, a diacetone alcohol, 1-methoxy-2-propanol, or combinations thereof The method of treating thermoplastic according to the invention includes (a) providing a near infrared absorbing dye that converts absorbed NIR radiation into heat without fluorescing significantly; (b) dissolving the dye into a substantially non-aqueous, organic solvent to form an ink composition; and (c) contacting a thermoplastic part with the ink composition. The contacting step may include painting, dry-burnishing, dip-coating, spraying, printing, and particularly ink jet printing. Examples of thermoplastic materials are polyesters, polyamides, polyolefins, polyurethanes and polycarbonates.